The present invention relates to a damper comprising a piston and cylinder section, each provided with fixing means for fixing to the parts moving with respect to one another, a cylinder part within which said piston moves being delimited in said cylinder and a chamber being delimited on either side of the piston, which chambers are connected to one another via a damping element, as well as a further chamber to which said displaced fluid can be transferred, said damper being constructed such that relatively high force is needed for displacement at low speed.
A damper of this type is generally known in the prior art and is used, for example, as rotation dampers in, for example, vehicles that run on rails. However, it is emphasised that the invention is not restricted to such rotation dampers. The invention in general relates to dampers having a so-called frictional force characteristic. That is to say, a high force is needed even at low speeds of displacement of the piston and cylinder with respect to one another. This is, for example, achieved in the prior art in that all fluid connections that make movement of the piston in the cylinder possible are provided with spring-loaded valves. That is to say, a certain fluid pressure must always be built up in order to overcome the resilience of the spring-loaded valves concerned. However, other dampers where displacement at low speed requires high force also fall under the invention.
As already indicated, such dampers are used, for example, as rotation dampers in vehicles that run on rails. In this context, the rotary movement of the bogies of such vehicles relative to the other part of the vehicle is damped as much as possible. As a result, it is possible to travel at higher speeds.
Because of the particular characteristics of such dampers, the fitting thereof is made appreciably more difficult. By way of example, a typical force for moving a piston and cylinder relative to one another is greater than 500 N. In the prior the art hydraulic aids are known by means of which the damper and thus, in particular, the fixings thereof accurately acquire the same spacing as the fixing supports on the vehicle that runs on rails. Sometimes it is also possible, when first fitting, to match fixing points on the vehicle that runs on rails to the distance between the fixings for the damper. However, if fitting is carried out at a later date, that is to say during a major or minor service, such possibilities do not exist and it is necessary to use special tools.
In the prior art, attempts have also been made to construct the supports by means of which such dampers are mounted on the vehicle that runs on rails such that they are adjustable in some way or other. However, appreciable costs are associated with this, whilst the construction has to be made much heavier.
The dampers described above must be distinguished from dampers for damping the movement of a vehicle wheel, such as, for example, are described in GB 2 159 234 A. In the unfitted state, the two parts of the dampers can be moved by hand. This British patent shows an additional channel for connecting the chambers located on either side of the piston. The valve contained therein can be operated electrically, as a result of which the damping characteristics can be changed while the vehicle is travelling.
A hydraulic, height-adjustable device is described in U.S. Pat. No. 5,362,034. With this device the piston does not delimit two chambers that communicate with one another via a damping element. Depending on the quantity of fluid that is present above the piston, the seat height of a seat can be adjusted. This quantity of fluid can be controlled with the aid of a hand-operated valve.
The object of the present invention is to improve the rotation damper described above such that simple fitting is possible, that is to say the distance between the fixings on the damper can be adjusted in a simple manner to the distance between the fixings on the vehicle concerned on which the damper has to be mounted.